Bruno Cvikl

Comparative study of I-V characteristics of the ICB deposited Ag\n-Si(111) and Ag\p-Si(100) Schottky junctions

Abstract The room temperature I-U characteristics of the ionized cluster beam, ICB, deposited Ag\n-Si(111) and Ag\p-Si(100) Schottky barrier junctions, for non zero Ag ions acceleration voltage Ua > 0 V, have been investigated. The effective Schottky barrier height (SBH) is observed to decrease if Ag is deposited on n-doped Si substrate but for Ag\p-Si junction shows an increase, relatively to the corresponding SBH values of Ua = 0 V ICB deposited junctions, respectively.

The drift-diffusion interpretation of the electron current within the organic semiconductor characterized by the bulk single energy trap level

The closed solution for the internal electric field and the total charge density derived in the drift-diffusion approximation for the model of a single layer organic semiconductor structure characterized by the bulk shallow single trap-charge energy level is presented. The solutions for two examples of electric field boundary conditions are tested on room temperature current density-voltage data of the electron conducting aluminum/tris(8-hydroxyquinoline aluminum/calcium structure [W. Brutting et al., Synth. Met. 122, 99 (2001)] for which jexp∝Va3.4, within the interval of bias 0.4 V≤Va≤7. In each case investigated the apparent electron mobility determined at given bias is distributed within a given, finite interval of values. The bias dependence of the logarithm of their lower limit, i.e., their minimum values, is found to be in each case, to a good approximation, proportional to the square root of the applied electric field. On account of the bias dependence as incorporated in the minimum value of the a...

On an example of the space charge limited conduction breakdown in relation to the current-voltage characteristics of a single layer metal/organic structure

The room-temperature current-voltage data of the hole conducting single layer poly-p-phenylene-vinylene indium tin oxide/poly-p-phenylene-vinylene (200 nm)/Al organic structure of Karg et al. [J. Appl. Phys. 82, 1951 (1997)], representing an archetype for (shallow) trap-controlled space charge limited conduction characterized by the current density proportional to the second power of the applied bias, j∝Va2, are used to calculate the spatial dependence of the internal electric field, the internal electric potential, and the total (free and trap) hole charge density within the organic layer. In contrast to the usual space charge limited current results, it is determined that these quantities are linearly distributed throughout the above structure. The breakdown of the Mott–Gurney approach is assigned to the usual, but in this case inappropriate, assumption of the boundary condition at the hole injecting metal/organic junction. It is shown that for the above stated structure the electric field at the anode/...

The microscopic model of Fermi level pinning in ionized cluster beam deposited Ag/n-Si Schottky structures

Abstract At metal–semiconductor interfaces, the Fermi level is usually found “pinned” in the bandgap. Schottky barriers of Ag/n-Si structures deposited by the ionized cluster beam (ICB) technique show a similar Fermi level pinning behaviour with respect to the metal atom acceleration voltage. We propose a simple model for the density of interface states at the disordered interface in an ICB Schottky structure. The Fermi level position inside the semiconductor bandgap is calculated as a function of increasing disorder.

On the role of the interface charge in non-ideal metal–semiconductor contacts

Abstract The bias dependent interface charge is considered as the origin of the observed non-ideality in current–voltage and capacitance–voltage characteristics. Using the simplified model for the interface electronic structure based on defects interacting with the continuum of interface states, the microscopic origin of empirical parameters describing the bias dependent interface charge function is investigated. The results show that in non-ideal metal–semiconductor contacts the interface charge function depends on the interface disorder parameter, density of defects, barrier pinning parameter and the effective gap center. The theoretical predictions are tested against several sets of published experimental data on bias dependent ideality factor and excess capacitance in various metal–semicoductor systems.

Fermi Level Pinning in Ag/Si Schottky Structures Prepared by Ionized Cluster Beam Technique

The observed variation of the Schottky barrier height in ionized-cluster-beam (ICB)-deposited Ag/Si Schottky structures is described within the framework of the disorder-induced gap stated theory (DIGS). The physical mechanisms determining the position of the Fermi level in ICB Schottky structures under different regimes of acceleration voltage are suggested, emphasizing the role of the local electronic structure.

Energy band shape of monolayer metal/organic/metal structures as determined by the capacitance-voltage method

The room-temperature differential capacitance of monolayer metal/organic-semiconductor/metal structures was derived. The derivation was based on two basic assumptions: (a) the rectifying metal/organic-semiconductor junction is characterized by the bias-dependent net excess charge density, induced at the interface, and (b) the charge flow within the organic layer is represented by the space-charge-limited current. The predictions of the derivations were compared to C-U data on an ionized cluster beam Ag-deposited 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) on indium-tin-oxide (ITO), Ag∕PTCDA∕ITO, sample obtained at 1 kHz and at room temperature. In addition, thorough analyses of published, room-temperature capacitance-voltage data for Al∕pentacene(60nm)∕ITO, poly(phenylene vinylene) Al∕PPV(200nm)∕ITO, poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene], Ca∕MEH‐PPV(40nm)∕Au, tris-(8-hydroxyquinoline) aluminum, Al∕Alq3(60nm)∕ITO, Ca∕Alq3(60nm)∕ITQ, and Ca∕Alq3(120nm)∕ITO organic-semiconduc...

The elimination of interface charge density singularity in single layer organic semiconductor structures

The arguments are presented that the assumption of a zero electric field at the charge carrier injection electrode/organic interface, as assumed by the current-voltage model of shallow traps occupying a single energy level within the organic semiconductor charge transport band as well as by the model of traps exponentially distributed in energy, is invalid in principle. In consequence of this fact, it is shown that the value of material parameters is strongly related to the bias dependent non-zero electric field at the charge-injecting interface. A set of published room temperature current-voltage data of a single layer, electron-only, metal/organic semiconductor structure is used in order to show explicitly that the singularity of free (or total) electron charge carriers at the injecting interface and the associated space charge limited current characteristics reflects an unrealistic assumption of the above two models. For the model of traps exponentially distributed in energy, the charge traps density a...

On the origin of interface induced charge density in ionized cluster beam deposited metal-semiconductor systems

The disordered interface electronic structure of ICB deposited Schottky structure is calculated using simple models for the metal and semiconductor. It is shown that the origin of the capacitance measurement detected bias dependent charge density can be ascribed to the presence of the disorder induced continuum of the electron states in the semiconductor energy gap and its coupling with the incorporated metal impurity states at the interface between the disordered interlayer and the regular semiconductor.

Analysis of the temperature dependent I-V characteristics of the ICB deposited Ag/Si Schottky structures

The current-voltage characteristics of Ionized Cluster Beam (ICB) deposited Ag/n-Si Schottky structures for nonzero acceleration voltage U/sub g/=300 V, 1 kV measured in the temperature interval T/spl isin/[300 K, 150 K] are analysed in order to identify possible different charge transport mechanisms on the samples. In the high temperature interval the charge transport is well enough described within the thermionic emission theory framework (TE), whereas in the low temperature interval (T<200 K) the suitable description of the transport is obtained assuming conduction through deep impurity levels and hopping process between continuously destructed localized electron states in the silicon band gap. It is argued that the addition transport mechanisms are induced by the disordered interfacial control layer (DICL) form by the energetic Ag ion incorporated into silicon crystal lattice situated between the metal and the ordered part of the semiconductor.